Hi thousandsunnysink and welcome to the forum. I'm glad your guy is happy. Mosquito larvae is good but as you've learned, be sure to rinse them off before feeding them.
Also, you might want to try pellets for food instead of flakes. Good brands to try are Omega One Betta Buffet Pellets and New Life Spectrum Betta Formula Pellets. You can usually get New Life Spectrum at Petco. Also, Top Fin Color-Enhancing Betta Bits from Petsmart are a decent food.
I'm glad your guy is bubblenesting already. Sadly, you will have to destroy his nest to do a water change. It happens to all of us. One of my guys only builds a bubblenest the day before a water change. They will get over it and build another one. Water changes are much much more important than a bubblenest. Since you're new here, I'll give a quick rundown on water changes. Depending on the size of his tank, you will want to do at least two water changes a week. Here's how it breaks down:
1 gallon tank: 90-100% every other day
2-3 gallon tank, no filter: one 50% and one 100% a week
2-3 gallon tank, filter: one 25% and one 50% a week
5 gallon tank, no filter: one 25% and one 50% a week
5 gallon tank, filter: one 50% a week
If you have anything smaller than 1 gallon, that's too small, you will have to change the water every single day. If you have a 10 gallon tank, it depends on whether or not he has tankmates.
If you have any questions, don't hesitate to ask.